1. Technical Field
The present invention relates to copper alloy foils, flexible printed circuit boards using the foils, and methods for producing copper alloy foils.
2. Description of Related Art
Known copper alloys for foils include copper-zirconium alloys. For example, PTL 1 proposes a copper alloy foil with improved electrical conductivity and ultimate tensile strength produced by hot-rolling an alloy containing 0.01% to 0.50% by weight of zirconium and having an oxygen content of 10 ppm or less to a predetermined thickness and then repeatedly subjecting it to cold rolling with intermediate annealing to a thickness of 35 μm or less at a rolling ratio of 90% or more. This copper alloy foil achieves a high strength up to 530 MPa. In PTL 2, on the other hand, the present inventors have proposed a copper alloy containing 0.05 to 8.0 atomic percent of zirconium and having a two-phase structure in which copper matrix phases and eutectic phases of copper and a copper-zirconium compound are layered on top of each other and in which the adjacent copper matrix phase crystal grains contact intermittently, thus achieving a high strength up to 1,250 MPa.